The common seal pupping season peaks in June and July. Pups weigh approx. 10 kgs and measure 85cm long at birth. They are born with their adult coat (black or brown in colour), as the white natal-coat is usually shed before birth, and can swim immediately, sometimes they are even born in water. A mother is attentive to her pup and stays close during the weeks she nurses it, often carrying them on their backs, or forcing them under the surface if danger threatens.

The pup feeds on the mothers milk which is extremely rich (45% fat), and suckling takes place either on land or in water. However, the care lasts for a very short time and at 4 weeks old the mother weans her pup and it is then completely independent from its mother. At this stage the pup will weigh between 20kgs and 30kgs. The pups have to then learn to catch fish, they do this by instinct.

Seals feed on a wide variety of fish and invertebrates, taking species which are locally abundant and easy to catch. In Scotland, Gadoid fish, particularly Whiting and Saithe, Herring and Sand-eels are important. Molluscs, such as Whelks and Octopus are also eaten.